Patent GB-809615-A (GB)
Title: Improvements in or relating to radio direction indicating systems
Inventor: PARKER ERIC
IPC: G01S7/00
Filed: 1956-08-02
Abstract: 809,615. Radio navigation. DECCARECORD CO. Ltd. July 31, 1957 [Aug. 2, 1956], No. 23934/56. Class 40 (7). In a radio beacon system a 1000 c/s. pulse train generated by an oscillator 12 and trigger circuit 13 modulates a microwave beacon transmitter 10 coupled to a narrow-beam aerial 14 rotated by a motor 17 and a 1000 c/s. sinusoidal reference signal (or subharmonic thereof) derived from the oscillator 12 modulates a V.H.F. or U.H.F. transmitter 20 coupled to a separate aerial 22, the phase of the reference signal being varied synchronously with the beam rotation by means of a phase shifter 18 controlled by the motor 17. At a mobile receiver the detected reference signal is applied in phase-quadrature to the X and Y deflectors 35, 36 of a cathode-ray tube 37 to produce a circular trace which rotates synchronously with the beacon beam aerial 14, the trace being intensity or deflection modulated by the bearing pulses received when the beam sweeps past the receiver thereby indicating the bearing of the receiver from the beacon. The V.H.F. beacon aerial 22 radiates a beam which is wider than that produced by the microwave aerial 14, the two beams being rotated in synchronism. The transmitter 10 and aerial 14 may form part of a conventional microwave pulse radar comprising a duplexer 15 and display 16. In a modification, Fig. 2 (not shown), interference from other pulse radars is prevented by applying the bearing pulses to the cathode-ray tube through a gate circuit which is opened by gating pulses derived in the receiver from a 1000 c/s. control signal produced at the beacon directly from the oscillator 12, the reference and control signals being transmitted on different sub-carriers modulated on to the V.H.F. carrier. The use of sub-carriers can be avoided by transmitting the reference or control signal as a subharmonic of 1000 c/s. and then multiplying up to 1000 c/s. in the receiver; also the bearing and gating pulses may be applied respectively to the grid and cathode of the cathode-ray tube such that the trace is intensified only when the two sets of pulses are coincident. A fine but ambiguous bearing indication may be provided by multiplying the frequency of the received 1000 c/s reference signal by a factor n (e.g. n = 12), Fig. 3 (not shown), or by transmitting from the beacon an additional " fine " reference signal comprising (1) a 1000 c/s. signal whose phase variation is n times that of the normal " coarse " reference signal, the fine and coarse reference signals being transmitted on different sub-carriers of the V.H.F. carrier, Fig. 4 (not shown), or (2) a signal obtained by frequency multiplication of the coarse reference signal. When fine and coarse reference signals are produced at the beacon they may be transmitted simultaneously or sequentially. The fine and coarse displays may be produced selectively by a manual switch or sequentially by a cyclic switch, the amplitudes of the fine and coarse reference signals being adjusted to produce corresponding circular traces of different radius, Fig. 5 (not shown); the indication may be read off by a pair of geared pointers (gear ratio n) rotatable by a single knob and coupled to a drum ype counter giving a numerical indication of the bearing.